Detailed knowledge of thickness and electrical properties of thin oxide (dielectric) layers on semiconductor wafers and semiconductor substrate interfaces to these layers is crucial in predicting device parameters that could be fabricated using any given semiconductor technology. Characterization of dielectric layers and their interfaces to the substrates may be needed at different stages of production from blank wafers to product wafers. The greatest challenges for the measurements of dielectric layers properties represent product wafers where limited test areas sizes, exact locations of test sites and extraordinary precautions in handling and protecting the wafers are imperative.
The most successful solutions for the measurement of the above dielectric layer properties known in the art are offered by contact methods with one electrical means applied to the bottom surface of the wafer and another electrical means applied to the measurement site over the top of the wafer. To obtain well-defined contact area of the conductive probe that is applied on the top of dielectric layer the elastic deformation of the probe tip may be used as described in References [1,2]. Another opportunity is offered by mercury probe described in Reference [3] where well-defined contact area can be obtained in repeated measurements with conductive strained liquid electrode. An apparatus to perform similar measurements that effectively uses plastic deformations of the probe tip is disclosed in Reference [4].
All of the techniques listed in References [1–4] may not suit well the challenges urged by the necessity to characterize thin dielectric layers on product wafers. Plastically deformable probes may not suit well to a limited size and exact positioning of the probe tip at the test site on product wafers. Mercury probe does not meet the requirements of non-contamination, while elastically deformable probe tips (References [1,2]) may introduce uninvited excessive pressure on dielectric and even destroy the dielectric layer that reaches several tens of Angstrom thickness for modern technologies.
The invention described below allows achieving a highly repeatable contact area for the above measurements via aligning the contact electrode to the wafer surface locally at the measurement site with substantially reduced pressure on the surface of the dielectric compared with the contact measurement techniques known in the art.